To investigate the factors that influence the probability of clinical cavitation at radiolucent areas of proximal surfaces of posterior teeth, 108 molars and premolars with varying depths of proximal radiolucency were examined clinically, after cavity preparation on the carious contiguous tooth surfaces. The data obtained were subjected to logistic regression analysis with cavitation as the dependent variable, while age, tooth type and past caries experience (DMFT and DFS) were independent variables. When proximal radiolucency was confined to the outer half of enamel, there was no cavitation, but when it extended to the amelodentinal junction and the outer and inner half of dentine, there was cavitation in 19.3, 79.1 and 100% of cases, respectively. Moreover, there was a statistically significant relationship between the probability of cavitation, depth of radiolucency and age, suggesting that these should be among the main factors considered when restorative management of a radiolucent proximal surface of a posterior tooth is contemplated.